IBM zSystems DFLTCC: Support inflate with small window

IBM zSystems DFLTCC: Support inflate with small window

There is no hardware control for DFLTCC window size, and because of
that supporting small windows for deflate is not trivial: one has to
make sure that DFLTCC does not emit large distances, which most likely
entails somehow trimming the window and/or input in order to make sure
that whave + avail_in <= wsize.

But inflate is much easier: one only has to allocate enough space. Do
that in dfltcc_alloc_window(), and also introduce ZCOPY_WINDOW() in
order to copy everything, not just what the software implementation
cares about.

After this change, software and hardware window formats no longer
match: the software will use wbits and wsize, and the hardware will use
HB_BITS and HB_SIZE. Unlike deflate, inflate does not switch between
software and hardware implementations mid-stream, which leaves only
inflateSetDictionary() and inflateGetDictionary() interesting.